1. Field of the Invention
The present invention relates primarily to dockside cranes utilized in cargo container handling operations for transporting cargo containers between the ship and shore. More particularly, the present invention relates to a wire rope reeving system for cargo container lifting spreader apparatus which are translated by said cranes. Still more particularly, the present invention relates to twin container lift apparatus for engaging two containers by independent lifting spreaders for simultaneous side-by-side movement and for lifting and lowering said two cargo containers, simultaneously and independently, by a single wire rope reeving system, while the containers are suspended at one location or being transported horizontally by the crane.
2. Description of the Prior Art
The utilization dockside of various types of cargo container handling gantry cranes, or quay cranes, for the purpose of loading and unloading of cargo container transport ships, is highly and diversely developed in the prior art. The reason is that shipping companies wish to reduce the time a ship spends in port involved in berthing operations (offloading and loading) in order to increase the efficiency of each vessel.
Quay crane container handling rates are measured in cycle rates. Unsteady quay crane operations result because the cranes move containers different distances depending upon the deposition location of the container on a ship causing varying the cycle rates. For example, as a quay crane loads or unloads each column of containers spaced across the beam of the ship, the hoist travels a longer distance outboard for each successive column of containers and lowers and hoists longer for each container located deeper in the stack. The increased traveling distance and stationary time for the hoist, for each successive container, adds to the container handling time and the resulting cycle time. Increasing productivity through reducing a ship's down time is essentially accomplished by permitting ships to be unloaded and loaded faster. Efforts are continuously being made to further this objective, and the present invention of concurrent multiple container handling is still another advancement in these efforts.
However, despite the numerous designs, structures, and forms of cargo container handling cranes disclosed by the prior art, which all have been developed for the accomplishment of the specific objectives, purposes, and requirements of reducing a ship's down time, the devices and apparatus which have been heretofore devised and utilized consist basically of familiar, expected, and obvious, configurations, combinations, and arrangements of well-known methods and machinery. This will become apparent from the following consideration of the closest known and relevant prior art.
Reference is made to FIG. 1 of the drawings which shows a typical dockside berthing operation for a ship. The primary container handling equipment is comprised of one or more quay cranes 11 which move on rails along the wharfs edge 13. A retractable boom or gantry 15 extends between at least two pickup and deposition positions such as a dock and a ship 17. The gantry in operative position is cantilevered outboard from the dock to extend over a berthed ship. The crane has a transport trolley or trolleys 19 mounted thereon for reciprocating travel on rails mounted on the gantry. Cargo shipping containers which have been unloaded or are to be loaded are temporarily stored in a stacking yard proximate to the ship loading berths.
In ship loading operations, cargo container transporters 21, such as chassis trucks, trailer trucks, or automatically guided vehicles (AGVs), deliver the containers 23 from the stacking yard to dockside. There, the quay cranes lift the cargo containers 23 from the dockside container transporters, or from an intermediate buffer mechanism or crane, and move them up and over the ship 17 where they are lowered into shipboard cells. The reverse occurs in ship unloading operations; the quay cranes access the shipboard cargo containers from above the ship and move them dockside and to the ground level or onto dockside transporters or intermediate buffer container holding mechanisms.
To decrease the cycle rate and increase the efficiency of the berthing operations, cranes were developed to transport two containers simultaneously between a ship and dockside. In 1970, a system for handling two containers simultaneously, end to end, or in tandem, was patented (U.S. Pat. No. 3,536,351 to Zweifel et. al.) by the predecessor company to the present assignee. Many variations followed.
A problem with those designs developed when increased and variable lengths of containers were put in use. When the standard length of a container was 20 feet, a crane could easily lift a pair of containers end-to-end. However, when container lengths commonly reached 40 feet, two containers of that length could not be lifted end-to-end by the quay crane apparatus disclosed by the prior art patents for several reasons. The containers would extend more than 20 feet past the ends of the lifting spreaders with only 20 feet of one end of each engaged by a spreader. The loads were too great. Lifting just one 20-foot container without another container in the other tandem spreader imposes a severe imbalance on the crane gantry. Obviously cranes can be designed to handle such imbalances but that requires a reinforced crane structure or a different crane design.
Early on it was determined that twin lifting of two containers solved the imbalance problems. Japanese patent S54-6267 discloses this arrangement (in 1979). However, the container handling cycle rates for the tandem or twin lift methods for cargo container handling can be improved still further for reducing cycle times. The twin lifting cargo container handling crane contemplated according to the present invention departs substantially from the conventional concepts and designs taught by the prior art, and, in doing so, provides a wire rope reeving apparatus primarily developed for the purpose of increasing still further the efficiency of ship berthing operations. It accomplishes the result in a different and improved manner and with a less expensive machinery requirement than the methods and apparatus of the prior art.
The present invention is a further improvement on these inventions and a substantial improvement for reducing crane cycle times. It increases still further the efficiency of a twin lift capable cargo container handling crane by permitting lifting and lowering the containers concurrently and independently with a single wire rope reeving system.